It sounds rather undignified, from a sheep's perspective, but it's all in the cause of saving the planet.

Hundreds of Australian sheep are to have their burp outputs measured by scientists who are hoping to breed a burp-less variety.

The world-first study is being led by scientists from the Sheep Co-operative Research Centre at Glen Innes in northwest New South Wales.

Sheep from 20 genetic lines will be fed, then shepherded into a booth where their belches are evaluated and compared.

Australian agriculture is responsible for 16 per cent of the country's greenhouse gas emissions, and two-thirds of those are methane from farm animals.

Around the country, scientists are experimenting with ways to reduce methane emissions, by varying sheep's diet and the microbes in their guts.

The team at Glen Innes hopes genetics may prove the key.

"We find sheep that do sit underneath the line in terms of how much methane they produce, compared to predictions, and sheep that are over the top," Roger Hegarty from the research centre told the Australian Broadcasting Corporation. "We're looking for natural [genetic] variations, so we'll steer the population that way."

In Australia, the highlighting of livestock's contribution to climate change has prompted campaigns for meat-eaters to shun lamb and beef in favour of kangaroo. Kangaroos emit very low levels of methane.

Another scientist involved in the sheep genetics study, John Goopy, said it was a common misconception that the methane produced by livestock was through flatulence.

"Ninety per cent of the methane that sheep and cattle and goats produce comes from the rumen, and that's burped out," he said.

Australia has about 92 million sheep in Australia, slightly more than four per person. In New Zealand the sheep population numbers more than 43 million - more than 10 per person.

Scientists said they had to proceed with care.

"Methane is the exhaust from livestock and, just as you can't put your hand over the exhaust pipe of a car and expect it to keep running, we're treading carefully to reduce emissions without causing other problems," said Dr Hegarty.